The present disclosure relates to a developing device incorporated in image forming apparatuses such as a copier, a facsimile, and a printer, and an image forming apparatus including the same, and in particular, the present invention relates to a method for reducing problems caused when toner is supplied, such as insufficient image density and fogging.
Known as conventional developing methods using a dry toner in an image forming apparatus employing an electro-photographic process are: a single-component developing method not using a carrier; and a two-component developing method of, by using a two-component developer for charging a non-magnetic toner with a magnetic carrier, developing an electrostatic latent image on an electrostatic latent image carrier (photosensitive body) with a magnetic brush of a toner and a carrier formed on a developing roller.
In a developing device, toner is consumed in a developing operation. Hence, there has been proposed a developing device in which, for the purpose of supplying toner to compensate for the amount consumed in a developing operation, a developer supply member is provided inside a developing container to supply developer to an agitating/conveying member.
For example, there has been known a developing device including first and second agitating/conveying members that agitate and convey developer, a developer supply member that rotates in the same direction as the first agitating/conveying member to supply the developer to the first agitating/conveying member, and a developing container that accommodates the first and second agitating/conveying members and the developer supply member. The developing container is provided with a supply section for supplying the developer from the developer supply member to the first agitating/conveying member. With this structure, by the rotation of the developer supply member, the developer is supplied from the developer supply member to the first agitating/conveying member in the supply section.
In such a developing device, toner is consumed through a developing operation. Hence, inside the developing device, there is provided a toner sensor that detects toner concentration (or toner amount), such that new toner is supplied to compensate for the amount consumed through the developing operation.
Here, when the developing device is operated continuously for a long time with a small amount of supply toner, as in a case where an image of a low printing rate is repeatedly printed and in a case where printing operations are repeated in an intermittent manner, mechanical stress on the toner circulating inside the developing device increases. As a result, electric charge on the toner in the developing device increases.
If, in this state, printing is performed at a high printing rate or continuously, initial toner charged to a comparatively low level is supplied into the developing device in a short period of time, and thus toner with a broad charge distribution is supplied to a developing roller, and this results in defective images such as those with insufficient image density and those with fogging.
To deal with this problem, there has been proposed a method for properly charging supply toner electrically, and there has been known a developing device in which, for example, a separation member and a pre-charging roller are provided in an agitating section, to thereby achieve stable charging of toner and reduce fogging occurring when toner is supplied anew.
There is also known a configuration where, in a developing device in which a supplying/conveying path, an agitating/conveying path, and collecting/conveying path are aligned substantially horizontally in this order from the vicinity of a developer regulating member, toner and carrier are supplied from a toner supplying position provided in the collecting/conveying path, and collected developer including the supplied toner and carrier is made to flow into the agitating/conveying path from a downstream-side end portion of the collecting/agitating path.